Delayed-action pulse repeater



92 mN W JITNM S Q Q Q Q N Allll m bN N m T T A INVENTOR A. S. GANO dPatented Oct 11, 1950 UNITED sTATEs PATENT OFFICE .DELAY-ED ACTION PULSEREPEATER Alfred S. Gano, White Plains, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication April 20, 1946, Serial No. 663,688

4 Claims.

This invention relates to a repeating device for electrical pulses andmore particularly to a delayed .action repeater, that is, one in whichan impressed input pulse gives rise to an output pulse after apredetermined delay interval.

An object of the invention is tomake the length of the delay.interval'substantially independent of the repetition rate of the pulsesto be repeated, even at repetition rates as high as 80,000 or morepersecond.

Another object is to make the length of the delay interval readilyadjustable over a range of values from a quarter of the repetitionperiod to three-quarters of that period, more or less.

Afurther object of the invention is to improve the operation of amultivibrator as a delayed action pulse repeater.

A feature of the invention is the use of a rectifying element in thegrid circuit nfone section of a multivibrator. Y

Another feature is the use of a variableanode loadresistor in a delaymultivibratorto vary the amount of the delay. 7

These and other objects and features of the invention are explained inmore detail in the following description and illustrated in theaccompanying drawing, the single figure of which is a schematicrepresentation of a pulse gener- 'ating and repeating system embodying'the invention. V V

The drawing shows a system comprising-a piezoelectric crystal um't illand a plurality of vacuum tubes II to "[5, inclusive. The vacuumtubesare all shown as 'triodes butmore elaborate tubes having additionalelectrodes may be substituted for the triodes if desired.

The "unit ill-comprises a conventional'cornbination of a" piezoelectriccrystal, supporting means therefor, and a paifof electrodesfbetweenwhich the, crystal is supported. The vacuum tube II together withthe-unit l and'interconnections constitute a conventional type ofpiezoelectrically controlled oscillation generator. The tubeiZ withassociated'circuit elements constitutes a pulse generator of the typecommonly known as a blocking oscillator and is arranged to becontrolled'in conventional manner, that is, synchronized'by the outputof the tube H. The tubes I3 and M with their associated circuitsconstitute a delay multivibrator which while to some extent conventionalin'circuit continuity, has a unique mode'of operation as willbedescribed in detail hereinafter.

The multivibrator is controlled by the blocking oscillator through arectifying element 16 in accordance with this vibrator is controlled bymeans of a variable resistor I! in the anode circuit of the tube 13,

also in accordance with this invention. The output of the multivibratoris impressed upon the grid circuit of the tube l5, which tube isintended to be representative of any suitable utilization circuit forthe delayed pulses from the multivibrator.

The blocking oscillator tube l2 has a cathode l8, a control grid [9 andan anode 20. A transformer is provided having three windings, wind- Thecathode I8 is connected to groundthrough invention and the delayinterval of the multia cathode resistor 29.

Coupling is provided between the blocking oscillator l2 and the grid ofthe tube l3 in the multivibrator through the rectifying element IB and aresistor 30. The grid of the tube l3, designated 3|, is connected toground through a resistor 32. The tube l3 has a cathode 33 and an anode34. The tube I4 has a cathode 35, a grid '36 "and an anode 31. i Theinternal connections of the multivibrator include a capacitor 38connected between the anode of the tube [3 and the grid of the tube I4.The anode 34 is connected to .the positive terminal'of the batteryZfil'through the variable resistor ll and a fixed resistor 39. The anode31 of the tube [4 is connected to the positive terminal of the battery24 through a pair of fixed resistors 40 and 4| across the resistor 4| ofwhich there is connected the primary winding of an output transformer42, the secondary windingof which is connected between the grid andcathode .of the tube l5. The grid 36 of the tube I4 is connected to thepositive terminal of the battery 24 through a resistor 43 of relativelylarge resistance value. The cathodes 33 and 35 are connected togetherand jointly grounded through a cathode resistor 44. A

capacitance 45 is shown in dotted lines connecte ingthe grid 36 andcathode 35 of the tube M.

The capacitance 45 represents the effective interelectrode capacitanceof the grid-cathode circuit of the tube l4 under operating conditions.

A coupling condenser 46 is shown connected to the junction point of theresistors 25 and 26 in the anode circuit of the blocking oscillator l2for the purpose of taking off a supplementary output from the blockingoscillator for utilization elsewhere.

The multivibrator is represented as having a pair of input terminals 41and 48, the former having the rectifying element I6 connected in seriestherewith and the latter being grounded.

In the operation of the system illustrated, the tube 2 l is energized bythe battery 24 to produce oscillations which energize the crystal whichin turn exerts a control over the oscillations of the tube H and tendsto stabilize the frequency of the oscillation in known manner. Theoscillations are fed through the winding 2| and are effective therein tosynchronize the operation of the blocking oscillator I2 with theoscillator II and crystal unit In, also in known manner. The pulsesgenerated by the blocking oscillator I2 appear in the winding 2i and aretransmitted through the resistor 30, the input terminal 41, the

rectifying element l6 and the resistor 32 to ground. The potential dropproduced in the resistor 32 by the current of the pulse from. theblocking oscillator is eifective to apply a positive pulse to the grid3| of the tube l3 thereby triggering the multivibrator.

In the absence of a triggering pulse, the multivibrator comprising thetubes l3 and [4 assumes a stable condition consistent with theconnection of the grid 36 of the tube I4 to the positive terminal of thebattery 24 through the resistor 43. This connection places a highinitial positive potential upon the grid 36, making the tube I4 normallyhighly conductive, passing anode and grid currents through the commoncathode resistor 44. The voltage drop in the resistor 44 impresses alarge negative potential upon the grid 3| of the tube [3 therebyrendering the tube l3 normally non-conductive. While this stablecondition of the circuit is being established, the capacitor 38 ischarged through the resistors 11, 39 and to a potential substantiallyequal to the full battery potential less the potential drop maintainedin l the resistor 44 by the combined anode and grid currents of the tubeHi, the negative side of the capacitor 38 being at the grid 36.

When a sufficient positive potential is superposed upon the grid 3l, asby means of a pulse through the resistor 32, the tube 13 is renderedconductive, thereb lowering the potential of the anode 34 and with itthe potentialof the grid 36 due to the charge on the capacitor 38. Thelowering of the potential of the grid 36 reduces or preferably cuts offthe current through the tube M. This action in turn reduces thepotential drop across the resistor 44 and enables the tube E3 tocontinue in the conductive condition even after the cessation of thepositive pulse in the resistor 32. The circuit remains in this newcondition with the tube l3 conductive and the tube 14 non-conductive,until the charge on the capacitor 38 has been reduced sufiiciently toenable the tube M to become conductive once more. When conduction beginsagain in the tube [4 a potential difference is generated across theresistor 4| which is transmitted through the transformer 42 to the tubel as a delayed pulse.

I During the portion of the cycle when the tube 13 is conductive, thecapacitor 38 is efi'ectively connected between the battery terminals inseries with the resistor 43, the anode-cathode path of the tube l3, andthe resistor 44. The polarity of this connection is such that thecapacitor 38 tends 4. to discharge and then to recharge in the oppositedirection toward the full battery potential. However, the cut-offpotential of the tube I4 is reached upon the grid 36 at about the sametime as the initial discharge is completed. @The time constant of thecircuit, for the values given, namely micromicrofarads in capacitor 38and one megohm in resistor 43, neglecting resistor 44, is 100microseconds. The discharge time until the cut-01f potential is reachedis only a fraction of 100 microseconds and depends upon the initialpotential at the grid 36. The initial grid potential in turn dependsupon a number of factors. Certain of the latter arise from the fact thatin practice the tube l3 does not constitute a perfect short-circuit fromits anode to its cathode when in the conductive condition. Accordingly,the anode 34 does not drop to the potential of the cathode 33. Thevalueto which the anode potential falls depends upon the relativeresistance values of the resistors I1, 39, 44 and the anodecathode pathof the tube l3 in the operating condition. The value of the anodepotential together with the potential difference between the anode ,34and cathode 33 determines the initial value of the potential of thegrid36 relative to the cathode 35, as it will be evident that thegridcathode potential difference in the tube i4 is the algebraicsummation of the anode-cathode potential difference in the tube l3 andthe potential difference between the terminals of the capacitor 38.

Another factor aifecting the initial grid potential is the sharing ofcharge between the capacitor 38 and the interelectrode capacitance 45.During the portion of the cyclein which the capacitor 38 is beingcharged through the resistors I1, 39 and 44, the interelectrodecapacitance 45 is substantially 'short-circuited by the grid-cathodepath of the tube l4. However, when the triggering pulse is impressedupon the grid 3| of the tube l3 and the tube 14 is consequently renderednon-conductive, the charge on the capacitor 38 is shared with thecapacitance 45 by means of current flowing through the anode-cathodepath of the tube 13. The resultant grid-cathode potential is less thanthe initial potential difference in the capacitor 38 and its amount isfurther lessened by the presence of the anodecathode potentialdifierence in the tube I3. In an embodiment which was builtand-successfully operated, the capacitance 45 amounted effectively to 30to 40 micromicrofarads. The time required for the grid 36 to reachcut-off was, found to range from a minimum of about 3 microseconds toamaximum of about 8 microseconds, depending upon the setting of thevariable resistor I 1 in the anode circuit of the tube l3. By means ofthe variable resistor I! theinitial potential of the grid 36 wasadjustable over a range from 90 to volts, more or less. The system wasfound to be operable at pulse repetition rates as high as 80,000 cyclesper second, which rate corresponds to a cyclic period of 12microseconds. Each impressed input pulse gives rise to an output pulseafter an interval which may be adjusted, as for example, within thelimits from 3 to 8 microseconds, more or less. Other repetition ratesmay of course be employed as desired and the time delay interval may beadjusted to a desired portion of the cyclic time, at least within widelimits.

Many conventional multivibrators have a coupling condenser or othercoupling impedance ele- .ment with one terminal connected to the anodeof the first tube and other terminal to the grid of thesec'ond tube andhave another coupling condenser o'r coupling impedance element similarlyconnected between the anode of the second tube and the grid of the firsttube. It has been customary in impressing a triggering pulse upon amultivibrator of this type to insert a unidirectional'conductor orrectifier between the triggering source and the grid of one tube in themultivibrator. The rectifier was arranged to conduct only in thedirection required to pass the triggering pulse. The presence of therectifier served to reduce or prevent reaction of the multivibrator uponthe triggering source.

In the type of multivibrator circuit disclosed herein, the couplingbetween the anode 31 and the grid 3! is accomplished by means of thecathode resistor 44. Accordingly, a change in anode current in the tubeI4, while it affects the potential difference between the grid 3| andthe oathode 33 by producing a potential drop in the resistor M, does notaffect the potential difference between the grid 3! and ground. Hence itwould seem feasible to connect a triggering source between the grid 3!and ground, with or without a rectifier, as desired, and withoutincurring a reaction of the multivibrator upon the triggering source. Inother words, the triggering source is decoupled with respect to thecoupling means which couples the anode 31 to the grid 3!. Experiencewith multivibrators of this type at moderate repetition rates hasconfirmed this conclusion.

At the frequencies and repetition rates here contemplated, namely 80,000cycles per second or more, however, the circuit was found not to worksatisfactorily without a rectifier between the triggering source and thegrid 3|. Applicant discovered that an unexpected improvement inoperation was obtainable by the use of the rectifier as specified.

'6 winding of relatively low directecurrent resistance between the gridandcathode of said first space discharge device constituting a grid leakpath of excessively low impedance, and a substantially unidirectionalconductor in series connection in series with said excessively lowimpedance grid leak path and having its direction of conductivity in thedirection of flowof the impressed control im'pulse, thereby blockingreverse current grid leakage through said path of excessively lowimpedance.

2. A multivibrator comprising two space di'scharge devices each havingan anode, a cathode and a grid, said cathodes being connected to acommon cathode terminal, a capacitor connected between the anode of thefirst said space discharge device and the grid of the second said spacedischarge device, a feedback resistor connected in a circuit betweensaid common cathode terminal and the grid of the first space dischargedevice, a grid leak resistor serially connected between the grid of thefirst space discharge device and the said feedback resistor, a source ofunidirectional control impulses, connections from said source to therespective terminals of said grid leak resistor, said last-mentionedconnections together with said control impulse source being ofrelatively low impedance compared with said grid leak resistor, and asubstantially unidirectional conductor in series connection with saidcontrol The element 16 between the input terminal 41 to act to give ahigher impedance looking back.

toward the input from the grid of the tube'l3 It has been found thatwith the rectifying element in the circuit as shown, therange of delayvariation which may be obtained is greater than otherwise could besecured. It hasbeen found also that the delay time is less influenced bythe amplitude of the input pulses and also less influenced by therepetition rate of the pulses when the rectifying element is employed.

What is claimed is:

1. A multivibrator comprising two spaced discharge devices each havingan anode, a cathode and a grid, a first coupling means coupling theanode of the first space discharge device to the grid of the second, asecond coupling means coupling the anode of the second space dischargedevice to the grid of the first,,a circuit decoupled with respect tosaid second coupling means for impressing a unidirectional controlimpulse upon the grid of the first space discharge device, adirect-current path including a transformer 3. A multivibratorcomprising two space discharge devices each having an anode, a cathodeand a grid, said cathodes being connected to a common cathode terminal,a source of current supply for said space discharge devices, a feedbackresistor connected between said common cathode terminal and the negativeside of said source of current supply, a capacitor connected between theanode of the first said space discharge device and the grid of thesecond said space discharge device, a fixed resistor connected betweenthe grid of the second space discharge device and the positive side ofsaid source of current supply, a primary winding of a load transformerconnected between the positive side of the source of current supply andthe anode of the second space discharge device, and an adjustable timingresistor connected between the positive side of the source of currentsupply and the anode of the first space discharge device.

4. vAmultivibrator comprising two space discharge devices each having ananode, a cathode and a grid, a first coupling means coupling the anodeof the first space discharge device to the grid of the second, a secondcoupling means coupling the anode of the second space discharge deviceto the grid of the first, a grid leak resistor in circuit between thegrid and cathode of the first space discharge device and havingsubstantially no coupling with said second coupling means, a controlimpulse supply path of relatively low impedance compared to said gridleak resistor, said control impulse supply path being in parallelconnection with said grid leak resistor, and with the grid cathode pathof said first space discharge device and including in series connectiona transformer winding of relatively low direct-current resistance, and'asubstantially unidirectional conductor serially connected with saidtransformer winding in said control impulse supply path and having itsdirection of conductivity in the direction of flow of the impressedtrans- ALFRED S. GANO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Stratton Aug. 1, 1944 Number 8Name Date Schrader et a1 Nov. 28, 1944 Miller et a1 Dec. 11, 1945 KoenigJuly 16, 1946 Ruhlig Aug. 6, 1946 Goldkey Aug. 13, 1946 Moe Jan. 14,1947 Yetter Apr. 8, 1947 Kahn Aug. 5, 1947

